The present invention relates to a laser projector, especially to a laser projector in which a first prism and a second prism are disposed on a scanning light path between a deflection component (microelectromechanical systems (MEMS) two-dimensional scanning mirror) and an imaging surface. An angle between the two prisms satisfies specific conditions. Thereby an image scanned and projected on the imaging surface achieves image distortion correction and image lift.
In a two-dimensional scanning projector with a single light spot, an incident light beam is off-axially delivered to a MEMS mirror for scanning and formation of an emitted light beam. Thus there are problems of image distortion and image lift. The image lift means the projected image needs to be moved upward. When the projector is placed on a desk or on a floor and in use, the lower half of the projected image is displayed on the desk or on the floor. The projected image is unable to be displayed on the whole imaging surface (such as screen) and this is inconvenient for users.
While a light spot is used together with a two-dimensional deflection component for scanning and projection, distortion on the imaging surface caused reduced quality of the image. The image distortion is caused by non-linearity between the scanning angle of deflection member and the distance to the imaging surface scanned, or oblique projection for image lift. In prior arts including U.S. Pat. No. 7,839,552 (CN100468123C), U.S. Pat. No. 7,957,047, U.S. Pat. No. 7,385,745, U.S. Pat. No. 7,256,917, U.S. Pat. No. 6,859,329, US2011/0141441, etc, a plurality of aspheric components or optical components with aspheric reflecting surfaces at fixed positions are used for correction of image distortion. However, aspheric components are difficult both in manufacturing and examination. Thus the cost is quite high. Moreover, the components should be assembled carefully in order to maintain respective positions of the components. The errors in the positions affect correction effect of the image distortion and change the size of the laser spot along the distance. Thus the assembly is quite difficult. As to U.S. Pat. No. 7,839,552 (CN100468123C), the optical components used (such as aspheric components or aspheric reflecting surfaces) are only for image distortion correction. Yet the present invention provides a laser projector in which a first prism and a second prism arranged in turn at a light path from a MEMS mirror to an imaging surface, and an angle between the two prisms satisfies specific conditions. Thus the scanned and projected image on the imaging surface are corrected and lifted up.
Refer to U.S. Pat. No. 7,878,658, a prism with multiple surfaces is used to guide light paths and correct image distortion. The prism includes an incident surfaces, an exit surface and internal surface for reflecting light beam. A light beam is incident into the prism through a first incident surface, reflected multiple times in the prism, and emitted out from the first surface at a designed angle. Then the light beam is incident into a deflection component, reflected and scanned and then entered the prism again through a second incident surface (original first exit surface). Next the light beam is emitted out from a second exit surface to form an image on an imaging surface. The second incident surface and the second exit surface are arranged in a non-parallel manner and such design is used for correction of image distortion. Moreover, the light path is guided by respective total reflecting inclined surfaces. However, the shape of the prism is quite complicated. The complicated processing of the prism results in high cost. Furthermore, the prism used is only for correction of image distortion and not related to image lift while the present invention includes a first prism and a second prism arranged in turn at a light path from a MEMS mirror to an imaging surface. An angle between the two prisms satisfies specific conditions so as to achieve both correction and lift-up of the image scanned and projected on the imaging surface.
Refer to U.S. Pat. No. 8,107,147 (WO2010/111216, CN102365573A) and US2010/0060863 (WO2010/030467, CN102150070A), both use mirrors for reducing image distortion. In U.S. Pat. No. 8,107,147, two scan mirrors are used for two dimensional scanning to generate a two dimensional image. A fold mirror for reflection is positioned on an output optic or combined with a scanning mirror to be formed on a common substrate. The output optic may be utilized to reduce or increase an amount of distortion in an image, please refer to FIG. 7 to FIG. 9 and description related to the output optic 710. Although the output optic 710 in some embodiment is a wedge optic that alters the output image, the output optic 710 can still be utilized to reduce or eliminate distortion an image generated, without the function of image lift. As to US2010/0060863, at least one wedge optic is disposed after the MEMS scanner. Refer to U.S. Pat. No. 8,107,147 (WO2010/111216, CN102365573A) and US2010/0060863 (WO2010/030467, CN102150070A), both use mirrors for reducing image distortion. In U.S. Pat. No. 8,107,147, two scan mirrors are used for two dimensional scanning to generate a two dimensional image. A fold mirror for reflection is positioned on an output optic or combined with a scanning mirror to be formed on a common substrate. The output optic may be utilized to reduce or increase an amount of distortion in an image, please refer to FIG. 7 to FIG. 9 and description related to the output optic 710. Although the output optic 710 in some embodiment is a wedge optic that alters the output image, the output optic 710 can still be utilized to reduce or eliminate distortion an image generated, without the function of image lift. As to US2010/0060863, at least one wedge optic is disposed after the MEMS scanner. Although two or more wedge optics are used in combination (refer to FIG. 2 and wedge optics 210, 218), they are utilized to correct and/or adjust chromatic aberration. The technique revealed in US2010/0060863 is unable to correct image distortion and lift the image at the same time. As to the present invention, two prisms are disposed in turn on a light path from a MEMS mirror to an imaging surface and an angle between the two prisms satisfies specific conditions. Thus both correction of image distortion and image lift are provided.
Refer to U.S. Pat. No. 8,159,735 (WO2010/021331, CN102132191B), a deflection apparatus is arranged to incline obliquely to perform an oblique projection onto a screen. The light beam is deflected by the deflection apparatus to be scanned and projected onto the screen obliquely. Thus the image can be displayed over the entire screen even the projector is placed on the desk or on the floor. However, the distortion of the image (such as trapezoidal distortion) is reduced or eliminated without provision of a projection optical system. No prism is disposed between the deflection component/apparatus (such as MEMS mirror) and the imaging surface (such as screen). The correction of the image distortion is by certain conditions of the direction of the incident light beam into the deflection apparatus. For example, as described in claim 1 and claim 2, a normal line of the reflection member of the deflection apparatus in the screen-center display state is tilted toward the negative direction side in the second scanning direction with respect to a normal line of the projection surface. A conditional expression “0.25<θmems/θin<0.75”in claim 3 is fulfilled. θmems is an angle formed by the normal line of the reflection member of the deflection apparatus in the screen-center display state and a normal line of the projection surface in the second scanning direction while θin is an incidence angle in the second scanning direction when a principal ray from the laser light source is incident on the reflection member of the deflection apparatus in the screen-center display state. Thus the technique revealed in the U.S. Pat. No. 8,159,735 requires no projection optical system while reducing distortion. In contrast, the present invention includes two prisms disposed between the deflection component/apparatus (such as MEMS mirror) and the imaging surface (such as screen) and the angle between the two prisms satisfies specific conditions for correction of image distortion and image lift. Thus the technique and features revealed in U.S. Pat. No. 8,159,735 are different from those of the present invention.
As to the disadvantages of the prior arts mentioned above, please refer to the following table.
disadvantagesnolimitedlowreducedcomplicatedimageeffectcomponenthighassemblylargedriveliftonprior artsdifficulty in componenttolerancecosttolerancevolumecontrolcontroldistortionU.S. Pat. No. 7,256,917▪▪▪▪▪U.S. Pat. No. 7,385,745▪▪▪▪▪U.S. Pat. No. 7,839,552▪▪▪▪▪U.S. Pat. No. 7,878,658▪▪▪▪U.S. Pat. No. 7,957,047▪▪▪▪U.S. Pat. No. 8,107,147▪▪U.S. Pat. No. 8,159,735▪U.S. Pat. No. 6,859,329▪▪▪▪▪US▪▪▪▪2004/0141221US▪▪▪▪2009/0251668US▪2010/0060863US▪▪▪▪▪2010/0253991US▪▪▪▪▪▪2011/0141441